Winter swimming in ice-cold-water is gaining increasing popularity. In Finland, there are c.a. 150000 regular winter
swimmers.
Winter swimmers believe that they achieve better health and well-being in many ways: better mood, less pains and aches, and less respiratory infections, for example. Research-based evidence to support these claims, however, is less conclusive, because studies have been quite small-scaled. When winter swimmers were compared to non-swimmers, no difference in health status were observed in a routine medical check-up, but their subjective well-being seems to be higher especially in person over 65 years. It may be that winter swimmers are happier already before starting the swims. A novice winter swimmer habituates to cold water already during the first
exposures, i.e. the cold discomfort is less intense (cold habituation). Further, the swimmer may develop hypothermic, insulative, or metabolic adaptation to cold depending on the intensity and frequency of the habit. Local and whole-body cryotherapy (including winter
swimming) have been used for a long time for pain relief in rheumatic diseases. Our results indicate that whole-body cryotherapy is at least as effective pain reliever as local cold therapies. Recently, also athletes have started to use cold water immersion for prevention of injuries, and for enhancement of recovery. After six weeks of repeated intense cold water exposures the proportions of lymphocytes, monocytes and TNF-alfa increased in young men. Also, resting levels of plasma IL-6, leucocytes, and monocytes were higher in habitual winter swimmers compared to non-swimmers. Acute exposure to cold water leads to an oxidative stress, but repeated exposures may lead to an improved antioxidant protection in a similar way as after exercise training. Thus, well-adapted winter swimmers seem to have a more favourable blood picture than non-swimmers. The hormonal responses to winter swimming have been very variable, but a common finding has been the significant increase in the concentration of plasma norepinephrine after swimming, which may be associated with pain alleviation. Whole-body cold exposure has been proposed to improve lung function in asthmatics, but the evidence is inconclusive. Swimming in ice-cold water leads to an increase in sympathetic activity, vasoconstriction, blood pressure, and myocardial work also in experienced winter swimmers. Therefore, winter swimming should be practiced with caution by persons with heart or lung problems